In recent years, thin display devices (flat panel displays), such as liquid crystal displays, have been widely used in the form of, for example, display devices for electronic devices, such as smartphones and tablet personal computers.
Such a display device includes a first substrate serving as an active matrix substrate, and a second substrate facing the first substrate. For example, a liquid crystal display includes a liquid crystal layer between first and second substrates. An organic electroluminescent (EL) display device includes a light-emitting layer between first and second substrates.
The display device includes a frame region extending along the perimeters of the first and second substrates and serving as a non-display region, and a pixel region formed inside the frame region. The pixel region includes a plurality of pixels each including a semiconductor element. A region of the first substrate corresponding to the frame region includes a plurality of wiring layers drawn from the pixel region. The wiring layers are parallel to one another.
The long wiring layers in the frame region tend to be electrically charged with a relatively large amount of electric charge. For this reason, electrostatic discharge (ESD) between an adjacent pair of the wiring layers causes a dielectric breakdown of an insulating layer covering the wiring layers.
To address this problem, an active matrix substrate described in PATENT DOCUMENT 1 has a frame region including a plurality of light blocking layers, a gate insulating layer, a semiconductor layer, a plurality of wiring layers, and a protection insulating layer. The light blocking layers are formed on the surface of an insulative substrate, and are made of metal. The gate insulating layer covers the light blocking layers. The semiconductor layer is formed on the entire surface of the gate insulating layer. The wiring layers cover the surfaces of portions of the semiconductor layer between adjacent pairs of the light blocking layers. The protection insulating layer covers the wiring layers. The semiconductor layer is formed in the same process step as the process step of forming semiconductor layers forming portions of semiconductor elements over a pixel region of the active matrix substrate.
This configuration allows the formation of transistors each including a portion of a corresponding one of the light blocking layers as a gate and portions of corresponding two of the wiring layers as a source and a drain, and thus allows the travel of electric charge from one of the corresponding two of the wiring layers through the semiconductor layer to the other one thereof when the potential difference between the charged wiring layers has increased. This reduces dielectric breakdown of the protection insulating layer due to the ESD.